Digital Moscow at Mos2.ru
Maybe this makes me an engineering geek, but this website is WICKED. Works rather like a Google Earth application (actually probably is based upon that) with maps of Moscow. Information for each region is available with a click of the mouse. You can zoom in on the map down to the street and building level. Photographs and comments are available for each region of Moscow.
You could waste lots of time just playing with this map, looking up landmarks and places you've been ... or places you've yet to visit.
Старые карты Москвы
If you are interested in historic maps of Old Moscow, Stariye Karti Moskvi (Old Maps of Moscow) is a good place to start. Contains scores of ancient maps of the city of Moscow, with a history discussion of each era and the changes in the city.
There is also Старинные карты России и Украины (Old Maps of Russia and Ukraine) which has a CD with over 600 ancient map images. Eight large color images are provided as samples.